Rapid thermal processing of semiconductor wafers involves placement of a semiconductor wafer in a reaction chamber which is thermally isolated from the wafer. The wafer is rapidly heated to a reaction temperature, with a reactant gas flowing over the wafer to induce reaction at the heated surface of the wafer. The wafer is then cooled and removed from the chamber and transported to further processing.
In rapid thermal processing, it is very difficult to ensure that the temperature distribution across the reaction surface of the wafer is dynamically uniform. Non-uniformities in the temperature distribution result in dislocations when growing single crystal layers, or other non-uniformities in the process occurring at the reaction surface.
Accordingly, technology has evolved to provide for a reasonably uniform temperature distribution across the reaction surface, taking into account radiant and convective heat losses. However, when flowing a reactant gas across a thermally isolated semiconductor wafer, convective heat loss tends to aggravate the uneven distribution of temperature. In particular, the convective heat loss around the edges of the wafer is greater than that in the center.
Dislocations in the semiconductor wafer are formed due to radial temperature gradients from the edge to the center of the semiconductor wafer. If the magnitude of tensile stress induced by the temperature gradients exceeds the yield stress of the semiconductor wafer material at the reaction temperature, plastic deformation of the growing layer and the substrate occurs. This plastic deformation results in dislocations or slip lines in the substrate and the grown layers.
Accordingly, it is desirable to have a method for rapid thermal processing of a substrate which reduces the thermal gradients in the substrate induced by convective heat loss.